Flash safety device in a flash apparatus

ABSTRACT

In the disclosed flash system, a flash voltage detector operates a switch which enables a flash triggering circuit only after the flash voltage reaches a predetermined value. In a preferred embodiment the switch includes a unidirectional element in series opposition to the triggering current flow. When the flash voltage is sufficiently high the switch passes forward current through the unidirectional element thereby decreasing the voltage drop thereacross and permits a triggering current.

United States Patent 1191 Nakamura Nov. 11, 1975 [5'41 FLASH SAFETYDEVICE IN A FLASH 3.751.714 8/1973 Cooper 315/241 P APPARATUS 3.764.84910/1973 Ohta 315/241 P 3.777.212 12/1973 Mashimo 315/241 P Inventor: enam ra, Urawa, Japan 3.778.672 12/1973 P61611616. 315/241 P 1. 3,814,9856/1974 Pecher et a1. 315/241 P [73] Asslgnee' g Kabushlk' Tokyo3.819.983 6/1974 Bjork 315/241 P apan [22] Filed: Aug. 23, 1973 PrimaryEraminer-Stanley D. Miller, Jr. pp No: 390,711 Attorney. Agent. orF1rnzToren, McGeady and Stanger [30] Foreign Application Priority Data57 ABSTRACT I Aug. 28. 1972 Japan 47-100203[U] A In the disclosed flashSystem a flash voltage detector operates a switch which enables a flashtriggering cir- [22] :18. C1. 315/241 P; 354/145 i only after the flashvoltage reaches a Predetep l lt. C1. H951) 41/14 mined value In apreferred embodiment the Switch 1 held of Search 3 15/ 1' 241 354/145includes a unidirectional element in series opposition to the triggeringcurrent flow. When the flash voltage [56] References is sufficientlyhigh the switch passes forward current UNITED STATES PATENTS through theunidirectional element thereby decreasing 3.593.061 7/1971 Takahata eta1. 315/241 the voltage drop thereacross and permits a triggering3.690.237 9/1972 Fuwa 354/145 current. 3.714.872 2/1973 Mashimo 315/241P 3.723.810 Mashimo 315/241 P 6 Clam, 1 Drawmg Flgure BOOSTER 3 4CIRCUITI\ g US. Patent Nv. 11,1975 I 3,919,593

BOOSTER 3 4 CIR u POWER SOURCE FLASH SAFETY DEVICE IN A FLASH APPARATUSBACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates to a flash safety device of a flash apparatus. I

2. Description of the Prior Art In known flash apparatuses, such asstroboscopic flash apparatuses, flashing is accomplished by boosting thelow voltage of the battery to a higher voltage and then applying theelectric charge to light a Xenon flash tube. The required flashintensity can be obtained only after the capacitor is suitably charged.Conventionally, a neon tube is used to indicate that the main capacitorhas been charged to place it in readiness for flashing the tube.Unfortunately, this requires the photographer to divert his attention tothe neon tube when he is taking continuous flash pictures. This issomewhat inconvenient and sometimes troublesome.

SUMMARY OF THE PRESENT INVENTION An object of the present invention isto provide a safety circuit for a flash apparatus in which a conductingelement such as diode, etc. is connected to a flashing voltage detectioncircuit of the flash apparatus to automatically prevent flashing of theflash apparatus when the apparatus does not have prescribed flashingBRIEF DESCRIPTION OF THE DRAWINGS The sole drawing is an arrangementdrawing of a safety circuit of the flash circuit apparatus according tothe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The sole drawing is an electriccircuit connection diagram to show an example of a safety circuit of theflash apparatus according to the present invention.

In the sole drawing 1 shows a low voltage actuation power source such asbattery, etc., 2 is a main switch of a flash apparatus, 3 is aconventionally known booster circuit, 4 is a rectifier diode, 5 is aflashing main capacitor, 6, 7 are bleeder resistors for detectingcapacitor terminal voltage, 8 is a neon tube, 9 is a Xenon tube, 10 is acurrent limiting resistance, 11 is a trigger capacitor, 12 is a triggertransformer, 13 is a triggering thyristor, I4, 15 are resistances, 16,19 are switching transistors, and l7, 18 are emitter, collectorresistances of the transistor 16. Member 20 is an FET, and 21 is aresistance connected in parallel with a temperature compensation diode22. Component 23 is an adjusting resistance, 24 is a switchingtransistor, and 25 is a diode as an one way conducting element.Reference character 25A identifies a circuit within a camera, wherein 26is an exposure meter circuit battery, 27 is a synchronizing switch, 28is a variable resistance which is varied depending on distance to anobject, 29 is an exposure meter, and CdS shows a light receiving elementto sense light from an object.

In the above arrangement, when the main switch 2 is turned ON, thevoltage as elevated by the booster circuit is impressed upon the maincapacitor 5 so that charging is started. Until the terminal voltage ofthe main capacitor 5 reaches a prescribed level, the bleeder voltagebetween the bleeder resistances 6, 7 will not become large, because itis in proportion to said terminal voltage. As a result the neon tube 8will not be lighted, therefore the transistor 16 remains OFF and so doesthe transistor 19.

As a result of the above, both FET20 and the transistor 24 are retainedin OFF state, therefore voltage will not be impressed on the transistor24. In this state when the synchronizing switch '27 is closed, since thediode 25 is connected in a reverse direction in a circuit of the triggerstarting circuit battery 26 synchronizing switch 27 resistance 14 SCR13diode 25 battery 26, starting current will not flow to the SCR13 and theXenon tube 9 is not lighted. When the terminal voltage of the capacitor5 is elevated to a prescribed value or higher, the neon tube 8 islighted and the tran sistors l6, 19 are turned ON. As a result currentfrom the power source 1 flows to the drain of the FET 20 and thecollector of the transistor 24. The diode 25 conducts the collectorcurrent of the transistor 24. The collector current of the transistor 24is almost proportional to the terminal voltageof the capacitor 5. Thusthe voltage across'the diode 25 will correspond to the voltage of thecapacitor 5 logarithmically with the compression characteristics of thediode 25. This voltage will be impressed upon to the circuit 25A in thecamera.

The exposure meter 29 is positioned based on the resistance value of thedistance resistance 28 and the sum of the voltage across the diode 25and the voltage of the battery 26, indicating the aperture value by itspointer position. Therefore, the diaphragm aperture of a camera isadjusted based on this indication. Thus the aperture value for flashauto-photographing can be set based on the distance to an object, andthe terminal voltage of the capacitor 5 which voltage corresponds to theamount of light to be emitted by the flash. Next, when the synchronizingswitch 27 is closed along with shutter release, the sum of the voltageacross the diode 25 and the voltage of the battery 26 will be impressedon the gate of the SCR13 through the resistance 14, the SCR13 is made toconduct and the Xenon tube 9 is ignited.

As has been explained above in the present invention the flashtriggering is prevented until the flash apparatus is placed in flashablestate by such one way conducting element as diode 25, etc. to preventunnecessary loss of energy at the power sourc'e by inadequate flashing,thus it is very useful in practical application. As the one wayconducting element, beside the above mentioned diode naturally suchelements as having one way conducting function by continuance of itsterminals for example SCR transistor, etc. can be used.

What is claimed is:

l. A flash apparatus comprising:

an electric power supply means,

a main capacitor coupled with said supply means to be charged thereby,

a flash tube coupled to said main capacitor,

a trigger circuit coupled to said flash tube and capable of ignitingsaid flash tube when the trigger circuit is enabled and a synchronizingsignal applied to the circuit, said circuit including a capacitor foraccumulating triggering energy, said capacitor being supplied withtriggering energy, said trigger circuit including means for applying theenergy to the flash tube when the circuit is enabled and thesynchronizing signal applied,

a voltage detecting means coupled to said main capacitor for detectingthe voltage across said main capacitor so as to emit an output therefromcorresponding to the voltage across said main capacitor,

a switching means connected between the output of said voltage detectingmeans and said trigger circuit andswitchable to an ON state when theoutput a of said voltage detecting means reaches a predetermined valueso as to enable said trigger circuit.

2.'A flash apparatus according to claim 1, wherein said voltagedetecting means contains a bleeder circuit coupled across the flashtube, said bleeder circuit being composed of a plurality of resistancesand having an output terminal, the output terminal of said bleedercircuit being coupled to said switching means.

3. A flash apparatus as in claim 1, wherein said switching meansincludes a constant voltage element connected-to the trigger circuit soas to produce a constant voltage in the trigger circuit when theswitching means is ON.

4. A flash apparatus comprising: i

an electric power supply means, a main capacitor connected with saidsupply means for charging 'thereby,

a flash tube coupled to said main capacitor,

a trigger circuit coupled to said flash tube and capable of ignitingsaid flash tube when the trigger circuit is enabled and a synchronizingsignal applied ,tojthe circuit, said circuit including a triggercapacfitor for accumulating triggering energy, means connecting saidcapacitor to the supply means for supplying triggering energy thereto,said trigger circuit including means connected with said flash tube andto said triggercapacitor for applying the triggering energy when saidcircuit is enabled and actuated so as to light said flash tube, v :avoltage detecting means connected with said main capacitor for detectingthe terminal voltage of said main capacitor so as to produce an outputtherea from corresponding to the terminal voltage of said maincapacitor,

-a switching means connected with said voltage detecting means andswitchable to an ON state when the output of said voltage detectingmeans reaches a predetermined value, a constant current circuit, saidcircuit being connected in said switching means and generating aconstant current when said switching means is turned to the ON state,

a unidirectionally conducting element, said element being connected withsaid constant current circuit in the forward direction and being turnedto an ON state when the constant current circuit generates constantcurrent so as to generate a constant voltage,

a synchronizing switch means coupled to said triggering circuit forproducing the synchronizing signal,

a trigger starting means in said trigger circuit for forming a path oftrigger starting current to cause said trigger starting current to flowtherethrough when said synchronizing switch means is turned to the ONstate so as to actuate said trigger circuit, said starting meansconnecting said unidirectional element within the path of said triggerstarting current to vary said trigger starting current, said startingmeans causing said trigger starting current to flow through said path inorder to actuate said trigger circuit when said unidirectional elementand said synchronizing switch means respectively are turned to the ONstate.

5. A flash circuit, comprising a gas discharge lamp, a main capacitorcoupled across the lamp, a capacitor charging circuit coupled across thecapacitor, a threshold voltage detector coupled across the capacitor andincluding a threshold voltage responsive switch whose state ischangeable in response to the capacitor voltage reaching a predeterminedvalue, a actuable trigger circuit coupled to the lamp and forming atrigger path, a unidirectional element in the trigger path,characterized in that said unidirectional element is directed to opposetrigger current flow and is connected to said detector to receiveforward current from the switch as the switch is switched when the maincapacitor exceeds the switchs threshold level.

6. An apparatus as in claim 5, further characterized in that the switchproduces a forward current in the unidirectional element correspondingto the capacitor voltage, and means in the trigger circuit responsive tosaid current to apply the current as an indication capacitor voltage. I

1. A flash apparatus comprising: an electric power supply means, a maincapacitor coupled with said supply means to be charged thereby, a flashtube coupled to said main capacitor, a trigger circuit coupled to saidflash tube and capable of igniting saId flash tube when the triggercircuit is enabled and a synchronizing signal applied to the circuit,said circuit including a capacitor for accumulating triggering energy,said capacitor being supplied with triggering energy, said triggercircuit including means for applying the energy to the flash tube whenthe circuit is enabled and the synchronizing signal applied, a voltagedetecting means coupled to said main capacitor for detecting the voltageacross said main capacitor so as to emit an output therefromcorresponding to the voltage across said main capacitor, a switchingmeans connected between the output of said voltage detecting means andsaid trigger circuit and switchable to an ON state when the output ofsaid voltage detecting means reaches a predetermined value so as toenable said trigger circuit.
 2. A flash apparatus according to claim 1,wherein said voltage detecting means contains a bleeder circuit coupledacross the flash tube, said bleeder circuit being composed of aplurality of resistances and having an output terminal, the outputterminal of said bleeder circuit being coupled to said switching means.3. A flash apparatus as in claim 1, wherein said switching meansincludes a constant voltage element connected to the trigger circuit soas to produce a constant voltage in the trigger circuit when theswitching means is ON.
 4. A flash apparatus comprising: an electricpower supply means, a main capacitor connected with said supply meansfor charging thereby, a flash tube coupled to said main capacitor, atrigger circuit coupled to said flash tube and capable of igniting saidflash tube when the trigger circuit is enabled and a synchronizingsignal applied to the circuit, said circuit including a triggercapacitor for accumulating triggering energy, means connecting saidcapacitor to the supply means for supplying triggering energy thereto,said trigger circuit including means connected with said flash tube andto said trigger capacitor for applying the triggering energy when saidcircuit is enabled and actuated so as to light said flash tube, avoltage detecting means connected with said main capacitor for detectingthe terminal voltage of said main capacitor so as to produce an outputtherefrom corresponding to the terminal voltage of said main capacitor,a switching means connected with said voltage detecting means andswitchable to an ON state when the output of said voltage detectingmeans reaches a predetermined value, a constant current circuit, saidcircuit being connected in said switching means and generating aconstant current when said switching means is turned to the ON state, aunidirectionally conducting element, said element being connected withsaid constant current circuit in the forward direction and being turnedto an ON state when the constant current circuit generates constantcurrent so as to generate a constant voltage, a synchronizing switchmeans coupled to said triggering circuit for producing the synchronizingsignal, a trigger starting means in said trigger circuit for forming apath of trigger starting current to cause said trigger starting currentto flow therethrough when said synchronizing switch means is turned tothe ON state so as to actuate said trigger circuit, said starting meansconnecting said unidirectional element within the path of said triggerstarting current to vary said trigger starting current, said startingmeans causing said trigger starting current to flow through said path inorder to actuate said trigger circuit when said unidirectional elementand said synchronizing switch means respectively are turned to the ONstate.
 5. A flash circuit, comprising a gas discharge lamp, a maincapacitor coupled across the lamp, a capacitor charging circuit coupledacross the capacitor, a threshold voltage detector coupled across thecapacitor and including a threshold voltage responsive switch whosestate is changeable in response to the capacitor Voltage reaching apredetermined value, a actuable trigger circuit coupled to the lamp andforming a trigger path, a unidirectional element in the trigger path,characterized in that said unidirectional element is directed to opposetrigger current flow and is connected to said detector to receiveforward current from the switch as the switch is switched when the maincapacitor exceeds the switch''s threshold level.
 6. An apparatus as inclaim 5, further characterized in that the switch produces a forwardcurrent in the unidirectional element corresponding to the capacitorvoltage, and means in the trigger circuit responsive to said current toapply the current as an indication capacitor voltage.